Copolymers of ethylene or of alpha-olefins (aka 1-alkenes) of C.sub.3 -C.sub.12 with alpha, beta-ethylenically unsaturated carboxylic acids have been disclosed in patents and/or literature for many years. Copolymers of the olefins with esters of the carboxylic acid monomers have also been disclosed. Various methods have been disclosed for the preparation of these copolymers, including the copolymerization with one or more other copolymerizable monomers to make copolymers which may be called terpolymers, tetramers, and the like. The various methods have involved, for the most part, at least one of the following:
(1) the use of batch reactions of the pre-combined monomers, which usually leads to a non-uniform, non-homogeneous product because of differing reactivity rates of the monomers unless the conversion of monomers to copolymers is held to a very low percent:
(2) the making of block copolymers by alternately charging first one monomer, then another, into the reactor, allowing each charge to attain a significant percent of completion before the subsequent charge is added, thereby producing a highly-ordered, essentially non-random, chain comprised of "blocks" of a given monomer between "blocks" of a different monomer, each block normally containing a plurality of the given monomer groups:
(3) the copolymerizaton of pre-combined monomers fed into a portion of a non-stirred (or poorly-stirred) reactor while removing the formed polymers at a point in the reactor which is distal from the feed point, such as in a tubular reactor, thereby continuously producing polymers which, because of the differences in reactivities of the monomers and the non-uniformity of the reaction mixture throughout the reactor, does not provide a copolymer which is homogeneous and uniform and can even create homopolymer molecules among the copolymer molecules, especially if one of the monomers becomes completely converted before the other monomer does;
(4) the grafting of an unsaturated carboxylic acid (e.g., acrylic acid, methacrylic acid, crotonic acid, etc.) or a dicarboxylic acid (e.g. maleic acid, maleic anhydride, fumaric acid, itaconic acid, and the like) onto an organic polymer, such as an olefin polymer or copolymer (esp. polyethylene); and
(5) feeding pre-combined monomers into a well-stirred, continuously operated autoclave reactor at substantially constant conditions of temperature, pressure, ratio of reactants, and flow-through, thereby continuously producing a copolymer which is substantially uniform and homogeneous, and in which the distribution of the acid groups along the polymer chain is random.
It is recognized in the art that copolymers made by polymerizing a mixture of monomers are often referred to as "interpolymers" because the monomers undergo polymerization simultaneously with each other, in contradistinction to those made by reacting a monomer with a previously formed polymer chain, such as block or graft copolymers.
For purposes of the preferred embodiment of the invention described hereinafter, the uniform, homogeneous, random copolymers are generally preferred, especially because batch-to-batch uniformity is more easily controlled in the present invention and because we have found that reactions involving the pendent acid groups are more readily optimized, due to the random distribution of the groups which avoids having a large population of the groups on adjacent carbon atoms along the polymer chain. Preparations of such copolymers are disclosed, e.g., in U.S. Pat. Nos. 3,520,861, 4,351,931, and 4,599,392. Even the so-called "non-random" copolymers produced in accordance with U.S. Pat. No. 4,248,990 have sufficient randomness of the pendent carboxyl groups to be useful in the present invention. An especially useful method for preparing an ethylene/unsaturated acid copolymer for reaction of the pendent carboxylic groups with an alkaline compound, such as caustic or an amine, is disclosed in U.S. Pat. No. 4,661,634.
It is known that ethylene copolymers having pendent carboxylic acid groups, especially ethylene/acrylic acid (or methacrylic acid) copolymers, can be reacted with NaOH or KOH to convert the --COOH groups pendent along the copolymer chain to --COONa or --COOK metal salt groups. It is also known that the pendent --COOH groups can be reacted with NH.sub.4 OH to form --COONH.sub.4 groups. The H.sup.+ groups can also be replaced with other cations. Furthermore, it is known that ethylene/acrylic ester copolymers can be hydrolyzed to convert the ester groups to --COOH groups or can be saponified to convert the ester groups to --COONa groups and the like. The metal salt forms of ethylene/acrylic acid (or methacrylic acid) are known as ionomers. The monovalent metal and ammonium salt forms of the pendent acid groups are known to cause the polymer to be more easily dispersed in water to form a stable dispersion.
The use of counter-ions or reagents to replace an amine group or an ammonium group or a given monovalent metal cation, such as an alkali metal, especially Na.sup.+ or K.sup.+, with a polyvalent metal cation, such as Co.sup.+2, Cu.sup.+2, Zn.sup.+2 Mg.sup.+2, and others is known. The Li.sup.+, Rb.sup.+, and Cs.sup.+ cations can be used as the monovalent cations, but they are less preferred and are more expensive than the Na.sup.+ and K.sup.+.
The use of aqueous dispersions of ethylene/acrylic acid and ethylene/methacrylic acid, and the like, and their salts, for treating fibers, such as wood, cellulosic or cotton fibers, and to treat paper and fabrics has been disclosed. Such treatments have involved applying the acid copolymers, or ionomers of the copolymers, to the fibers before shaping the fibers into a paper or fabric, or after shaping the fibers into a paper or fabric.
It is within the purview of the present invention to use a fine particle dispersion of any long-chain dispersible polymer comprising organic polymeric molecules having pendent acid groups which can be reacted with a reagent that replaces cations on the acid groups with cations which convert the dispersible polymer to a non-dispersible form; i.e., it is rendered non-dispersible in the liquid in which it had been previously dispersible.
This disclosure primarily relates the present invention with reference to the preferred carboxyl-containing ethylene copolymers, but the principle of converting a dispersible polymer having pendent acid groups to a non-dispersible form, by using a reagent which replaces cations on the acid groups, applies to other organic polymers, and provides useful modifications of fibers, fabrics, webs, paper, and the like.
We have now found that highly beneficial and unexpected results are obtained by applying the described polymers as dispersions to paper, nonwoven webs, yarns or fabrics (or to the fibers before making the paper, nonwovens, yarns or fabrics), and the like, while the polymers are in a dispersible form, e.g., the ionomer form (using a monovalent metal cation, ammonium, or amine form), then adding a reagent which converts the polymer to a non-dispersible form and "fixes" or "complexes" the polymer in place. Alternatively, the reagent which converts the polymer to a non-dispersible form may be applied to the paper, nonwovens, yarns or fabrics (or the precursor fibers of these) before the polymer dispersion is added.